In the semiconductor arts it is common that manufacturing sequences are particularly tailored to the type of devices being formed. For example, metal-oxide-semiconductor (MOS) devices may be formed using a first process flow and bipolar devices formed using a second, different process flow, each process flow being optimized for the particular type of devices for which it is being used. However, there are some circumstances where it may be desirable in order to optimize overall circuit performance, to have both types of devices available on the same chip, that is, within the same integrated circuit. This can create manufacturing difficulties since the process steps needed to provide optimized MOS devices and the process steps needed to provide optimized bipolar devices can be somewhat incompatible, that is, the steps needed to form one type of device can have deleterious effects on the other devices being formed in or on the same semiconductor substrate. Accordingly, there is a need for improved device structures and methods of fabrication that mitigate and/or overcome such difficulties.
Accordingly, it is desirable to provide an improved manufacturing method and structure wherein bipolar transistors can be advantageously formed in the same substrate with an MOS device manufacturing technology. It is further desirable that the methods, materials and structures employed be compatible with present day manufacturing capabilities and materials and not require substantial modifications of available manufacturing procedures or substantial increase in manufacturing costs. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.